Measurement unit for determining gas flow through a conduit and measuring means designed to be included in such a measuring unit

Abstract

A measurement unit for determining gas flow through a conduit by means of measuring pressure differential over an orifice arranged in the conduit (1), and to a measuring means designed to be included in such measurement unit. The purpose of the invention is to achieve a measurement unit and a measuring means which produce reliable readings and are of simple construction. This is achieved by means of an orifice centrally arranged in a section of the conduit (1) made as a flat circular disc (2) perpendicular to the central axis of said section. Round pressure measurement boxes (3) are arranged close to the sides of the disc. The inner chambers (13) of the boxes communicate with the space close to the disc and immediately outside the lateral wall (11) of the box via aperture means (10) between the lateral wall edge portion adjacent to the disc and the surface of the disc. The pressure chamber (13) inside each box defined by the box and the surface of the disc, is in communication with a pressure differential meter outside the conduit section via a flexible pressure differential meter outside the conduit section via a flexible pressure lead-out hose (8) coupled between a pressure lead-through nipple (7) in the wall of the box (3) and the meter. The diameter of the disc is at least 50% of the inner diameter of the conduit section (1) and the outer diameter of the box is at most 60% of the diameter of the disc.

I claim: 
     
       1. Measurement unit for determining gas flow through a conduit or duct by means of measuring pressure differential over an orifice means arranged in the conduit or duct, characterized in that said orifice means comprises within a straight, circular section (1) of the conduit, a centrally mounted, flat circular disc (2), the plane of which is perpendicular to the central axis of the section of conduit, said disc (2) having a diameter less than the interior diameter of the conduit section (1) but being at least 50% of said interior diameter, and in that on each side of the disc (2) there is arranged, coaxially to the disc, a rotationally symmetrical pressure measurement box (3) having a lateral wall (11) pointing towards the disc and which is arranged with its edge portion in close proximity to the surface of the disc, between said edge portion and the surface there being aperture means (10) through which a pressure measurement chamber (13) inside the box, and defined by the walls (11, 12) of the box and the surface of the disc, is in communication with the space in close proximity to the disc but outside the lateral wall (11) of the box, and in that in a wall of each box (3) there is a pressure lead-through means (7) with a portion outside the box to which there is connected a pressure lead-off line (8) which runs through the wall of the conduit (1) and can there be connected to a pressure differential meter. 
     
     
       2. Measurement unit according to claim 1, characterized in that the boxes (3) are two identical casings each with a cylindrical lateral wall (11) and an end wall (12) sealingly connected thereto and in which the pressure lead-through means (7) is mounted. 
     
     
       3. Measurement unit according to claim 1, characterized in that the boxes (3) are held in close proximity to opposite sides of the disc (2) by a bolt (4) passing through the centers of the boxes and provided with a nut (5), the longitudinal axis of said bolt coinciding with the central axis of the conduit section (1), said central bolt (4) passing through and being carried by a rubber gasket (6) which is mounted in an opening in the central portion of the disc (2) and which seals both against the disc (2) and the bolt (4). 
     
     
       4. Measurement unit according to claim 1, characterized in that the disc (2) is fixed in the conduit by means of legs (9) fastened to the edge portion of the disc and which extend preferably radially out from the disc and are fastened at their ends away from the disc to the inside of the conduit wall (1) preferably by means of angled foot members (14). 
     
     
       5. Measurement unit according to claim 1, characterized in that the aperture means consist of one or more narrow gaps (10) at the box (3) wall (11) edge portion in close proximity to the disc. 
     
     
       6. Measurement unit according to claim 1, characterized in that the aperture means consist of a plurality of small openings (10) or notches in the box wall (11) edge portion in close proximity to the disc. 
     
     
       7. Measurement unit according to claim 6, characterized in that the edge portion of each box (3) has a plurality of evenly spaced notches (10) along the entire said edge portion thus providing it with a toothed edge. 
     
     
       8. Measurement unit according to claim 1, characterized in that the lateral wall of each box (3) is a circular cylindrical lateral wall (11), the outer diameter of the box being at most 60% of the diameter of the disc (2). 
     
     
       9. Measuring unit according to claim 1, characterized in that the edge of each box (3) lateral wall (11) directed towards the disc (2) consists of an unbroken annular surface disposed in a plane parallel to the plane of the disc, that in each side of the disc there is in the region of the annular surface at least three spaced, raised heels or ridges (15) forming abutments against which said edge annular surface of the lateral wall rests, the arcuate, narrow gaps between the free annular surface and the disc (2) constituting the aperture means (10'), which are thus defined by the abutments, the annular surface and the surface of the disc. 
     
     
       10. Measuring means designed to be placed in a fluid flow in a conduit or a pipe, for measuring pressure differential over the means, characterized in that the means comprises a flat, circular disc (2) designed to be disposed transversely to the directional flow and that on each side of the disc (2) there is arranged, coaxially to the disc, a rotationally symmetrical pressure measurement box (3), the lateral wall (11) of which pointing towards the disc being arranged with its edge portion in close proximity to the surface of the disc, between said edge portion and the surface there being aperture means (10, 10') through which a pressure measurement chamber (13) inside the box and defined by the box wall (11, 12) and the disc surface is in communication with the space in close proximity to the disc but outside the lateral wall (11) of the box, and that in the wall of each box (3) there is a pressure lead-through means (7) to the portion of which outside the box a pressure lead-off line (8) can be connected.